End the match pattern with the number you are seeking, such as

  print "3-digits ending in 5" 
    if ( $number =~ m/\d{2}5$/ );
  print "4-digit number ending in 0 or 9"
    if ( $number =~ m/\d{3}[09]$/ );
  # as opposed to
  print "2 digits followed by a 3, but may have additional digits" 
    if ( $number =~ m/\d{2}3/ );
[download]

Hope that helps.

my $last_digit = 5;
if ($last_digit == substr $number, -1) {
    print "Matches!\n"
}
[download]

Or, similarly, use rindex:

if (rindex($number, $last_digit) == length($number) - 1) {
    print "Matches!\n"
}
[download]

There are many ways. Start here: How do I post a question effectively?

#!/usr/bin/perl
use warnings;
use strict;

my $predetermined = 6;

my @nums = qw(6 645 1086 1996 2015 2026);

for my $num (@nums){
    if ($num =~ /$predetermined$/){
        print "$num\n";
    }
}
[download]

-stevieb